The present invention relates to a process for lubricating a surface such as a mould, a conveyor belt, etc., for the manufacture of a glass article such as a receptacle, in which there is periodically deposited a layer of lubricant on the surface. The manufacture of glass objects, in particular hollow glass objects such as bottles, flasks, etc. . . . is usually carried out in accordance with two methods:
The first method, termed "blown-blown", in which a blank is formed by blowing in a first mould, this blank being then transferred to a second mould in which it is blown so as to assume its final shape.
The second method, termed "pressed-blown", in which a blank is formed by pressing a drop of glass or parison issuing from a hopper in a mould, this blank being then transferred to a blowing mould in which the hollow blank is blown so as to assume its final shape.
Flat glass objects are usually produced by pressing.
Irrespective of the method employed, the internal walls of the moulds in which the blanks are formed are regularly lubricated to permit an improved penetration of the glass and avoid cetain surface defects of the blank, which defects subsist on the finished receptacle. The technique still frequently employed at the present time in glassworks is a technique involving the manual lubrication of the moulds, which is not without danger for the handlers. This lubrication is usually carried out with an oil containing graphite in suspension.
In such a manual method, the operator has a tendency to deposit a large quantity of oil so as to reduce the frequency of the lubrications. This results in a soiling of the first blanks produced after each lubrication and considerably increases the losses in the manufacturing line. Further, a large amount of smoke in the working area is created.
It has been for a long time attempted to substitute for the manual lubrication an automatic lubrication in manufacturing lines of glass receptacles, without much success up to the present time.
French Pat. No. 1,285,586 discloses an automatic lubricating process for a closed mould in which the moulding apparatus is provided with lubricating passageways through which oil is injected into the mould before introducing the parison in the latter.
The introduction of oil by a manual or automatic process results in a great local pollution, since the oil burns upon contact with the moulds and gives off a thick black smoke charged with polyaromatic hydrocarbons. Now this pollution is found on the glass articles, the latter being coated with residues of incomplete combustion of the oil which do not burn in the air notwithstanding the high temperature at which the blank leaves the mould, which in practice forbids the lubrication before each introduction of a parison. If this lubrication is not effected before each introduction, there is a rapid decrease in the pollution but a corresponding increase in the surface defects of the glass article.
A solution has been proposed in U.S. Pat. No. 4,165,974 which comprises coating the internal surface of the moulds with a carbon fluoride so as to produce an anti-adherent layer on this surface. This process necessitates the disassembly of each mould, the treating thereof, and then its submission to a heat treatment before placing it back on the machine. Although the mentioned duration of lubrication is several hours, such a process requires a practically permanent human presence around the manufacturing machine with the obligation to frequently stop this machine for disassembling the moulds, lubricating them, remounting them, etc., which results in prohibitive manufacturing costs.
U.S. Pat. No. 4,409,010 discloses a process for lubricating moulds by a spaying of liquid oil onto the internal surfaces of the moulds, but the disclosed process does not avoid the drawbacks relating to the use of oil for the lubrication.
There is also another problem when using one of the processes described hereinbefore: when the glass receptacles leave the mould without a trace of greasy pollution, their surface state is usually poor, it of course depending on the quality of the surface of the steel mould. Although this quality is monitored, the receptacles usually have, when leaving the manufacturing line, a mat appearance of the "orange peel" type which is unsatisfactory to the client. This is why the applicant has developed a process for polishing the surface of glass artivles disclosed in the European Pat. No. 136,934 whereby it is possible to give a shiny surface appearance to these articles. Such a process, which is particularly required when producing receptacles of high quality, for example in the perfumery field, necessarily increases the manufacturing costs and it is at the present time desired, for the manufacturer of glass bottles or receptacles in respect of which the surface quality requirements are less strict, to obtain directly from the mould, a receptacle whose surface state is acceptable to the client.
U.S. Pat. No. 4,412,974 discloses a process for producing carbon black in which an acetylene jet is cracked in an air or oxy-fuel flame. This process has numerous applications. One consists in depositing a layer of carbon black on the walls of a mould, this layer having high lubricating and insulating qualities. Such a process is applicable in the glass-making field in particular for insulation against thermal and mechanical shocks of belts transferring glass objects issuing from the moulding machine and traveling for example to the machine for effecting a surface polishing with the flame mentioned above. In this way, harmful thermal and/or mechanical shocks of the glass receptacles leaving the moulds are avoided owing to the insulating properties of the produced carbon deposit.
It has however been found that by using the process disclosed in U.S. Pat. No. 4,412,974 for producing glass receptacles, results were obtained which were substantially equivalent to those obtained with the previously described techniques: the deposits of carbonaceous material usually permit a good lubrication but have the drawback of rapidly soiling the moulds and producing greasy deposits on the surface of the glass article, as in the case of the use of oil. No improvement on the surface state of the receptacle leaving the mould was found however relative to processes for greasing the imprints of the mould. On the other hand, it has been found, as described in French Pat. No. 25 70 364, that the use of the proces disclosed in U.S. Pat. No. 4,412,974, enabled the blank moulds to be correctly lubricated during their normal period of opening so that any adherence of the parison to the walls of the mould is avoided.